Waiting in main thread for a flag to be set by thread

#include<iostream.h>
#include <cstdlib>
#include <pthread.h>
using namespace std;

bool flag = false;

void* doStuff(void t)
{
	//does lots of stuff
	flag = true;
	
	//does lots of stuff. takes long time to do that
}
pthread_t threadCall(int t)
{
   pthread_t threads;
   int rc;
   int i;
      
      rc = pthread_create(&threads, NULL, doStuff, (void *)t);
      if (rc){
         cout << "Error:unable to create thread," << rc << endl;
         exit(-1);
      }

 return threads;

}

int main()
{
	int t =10;
	pthread_t thread= threadCall(t);
	
	//does some function calls
	while(!flag);
	
	//do some stuff when flag gets true.
	
	pthread_join(thread, NULL);
	return 0;
}

Select allOpen in new window

above is my code. I want to wait in main thread for flag to be set true by another thread as you can see here doStuff() function set the flag true.  In main thread, statement while(!flag); waits in busy waiting until flag get true.

Is there any other way to wait in main thread except this busy waiting.

Thanks in advance